MC44605(2000) Просмотр технического описания (PDF) - ON Semiconductor

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MC44605
(Rev.:2000)

High Safety, Latched Mode, GreenLine PWM Controller for (Multi) Synchronized Applications

ON Semiconductor 

Pin

1

VCC

2

VC

Name

3

Output

4

GND

5

Maximum Power Limitation

6

Over–Heating Detection

7

Current Sense Input

8

Demagnetization Detection

9

Synchronization and E.H.T.OVP Input

10

Oscillator Capacitor CT

11

Soft–Start

12

Cext (Disabling Block)

13

E/A Output

14

Voltage Feedback

15

Winding Short Circuit Detection

Programmation

16

Rref

MC44605

Pin Description

This pin is the positive supply of the IC.

The output high state, VOH, is set by the voltage applied to this pin. With a

separate connection to the power source, it gives the possibility to set by

means of an external resistor the output source current at a different value

than the sink current.

The output current capability is suited for driving a power MOSFET.

The ground pin is a single return typically connected back to the power

source. It is used as control and power ground.

This block enables to estimate the input power. When this calculated power

is detected as too high, a fault information is sent to the disabling block in

order to definitively disable the circuit.

This block estimates the MOSFET heating. When this calculated heating is

too high, the device gets definitively disabled (disabling block action).

A voltage proportional to the current flowing into the power switch is

connected to this input. The PWM latch uses this information to terminate

the conduction of the output buffer. A maximum level of 1 V allows to limit

the inductor current.

A voltage delivered by an auxiliary transformer winding provides to the

demagnetization pin an indication of the magnetization state of the flyback

energy reservoir. A zero voltage detection corresponds to a complete core

demagnetization. The demagnetization detection prevents the oscillator

from a re–start and so the circuit from a new conduction phase, if the

fly–back is not in a dead–time state. This function can be inhibited by

connecting Pin 8 to GND but in this case, there is a minimum off–time

typically equal to 3 µs.

Activating the synchronization input pin with a pulse higher or equal to the

negative threshold (typically –200 mV) allows the next switching period to

be reinitialized. The oscillator is free when connecting Pin 9 to GND.

When the E.H.T.OVP pin receives a voltage that is greater than 7.5 V, the

disabling block Cext capacitor is charged so that the circuit gets definitively

disabled if the Cext voltage becomes higher than Vref. This block is

incorporated to detect and disable the device when the synchronization

pulses are too high.

The free mode oscillator frequency is programmed by the capacitor CT

choice together with the Rref resistance value. CT, connected between

pin 10 and GND, generates the oscillator sawtooth.

A capacitor connected to this pin can temporary reduce the maximum

inductor peak current. By this way, a soft–start can be performed. By

connecting pin 11 to Ground, the MC44605 is shut down.

When a too high synchronization pulse voltage (E.H.T.OVP) or a winding

short circuit (WSCD) is detected, the capacitor Cext is charged using

a current source IDis– H. In the case of a MPL or OHD fault detection, Cext

is charged using IDis–L. If the Cext capacitor voltage gets higher than Vref,

the circuit is definitively disabled. Then, to restart, the converter must be

switched off in order to make VCC decrease down to about 0 V.

The error amplifier output is made available for loop compensation.

This is the inverting input of the Error Amplifier. It can be connected to the

Switching Mode Power Supply output through an optical (or else) feedback

loop or to the subdivided VCC voltage in case of primary sensing technic.

The W.S.C.D. block is incorporated to detect the transformer Winding Short

Circuits. This function is performed by detecting the inductor overcurrents

thanks to a comparator which threshold is programmable to be well

adapted to any application.

The Rref value fixes the internal reference current that is particularly used to

perform the precise oscillator waveform. The current range goes from 100

µA up to 500 µA.

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